As LCDs, one of many types of image displays, have been technically improved to provide wide viewing angles, high resolution, high response, good color reproduction, and the like, applications of LCDs are spreading from laptop personal computers and monitors to television-sets. In a basic LCD structure, a pair of flat glass substrates each provided with a transparent electrode are opposed via a spacer to form a constant gap, between which a liquid crystal material is placed and sealed to form a liquid crystal cell, and a polarizing plate is formed on the outside surface of each of the pair of glass substrates. In a conventional technique, a glass or plastic cover plate is attached to the surface of a liquid crystal cell in order to prevent scratches on a polarizing plate bonded to the surface of the liquid crystal cell. However, the placement of such a cover plate is disadvantageous in terms of cost and weight. Thus, a hard-coating process has gradually been used to treat the surface of polarizing plates.
When hard-coating treatment is performed on a transparent plastic film substrate to produce a hard-coated film, thermosetting resins or ionizing radiation-curable resins such as ultraviolet (UV)-curable resins are generally used to form a thin hard-coating layer with a thickness of about 2 to 10 μm on the transparent plastic film. If such resins are applied to a glass material, the resulting hard-coating layer can exhibit a pencil hardness of 4H or more. If a hard-coating layer with an insufficient thickness is formed on a transparent plastic film substrate, however, the pencil hardness of the layer can be generally affected by the substrate and reduced to 3H or less.
LCD applications have come to include home television sets, and thus it is easily expected that the users of general home television sets should handle LCD television sets in the same manner as in the case of glass CRT television sets. Glass CRTs have a pencil hardness of about 9H, which significantly differs from that of current hard-coated films. Thus, hard-coated films have been required to have higher hardness, even if it cannot reach a pencil hardness of 9H.
An increase in the hardness of hard-coated films is possible by increasing the thickness of their hard-coating layer. However, the increase in layer thickness can cause a problem in that the particles are completely buried in the hard-coating layer and cannot provide sufficient antiglare properties. The addition amount of the fine particles may be increased to improve the antiglare properties, but in such a method, the number of the particles is increased in the layering direction, which causes a problem of high haze value. Recently, therefore, methods for overcoming the drawbacks of trying to achieve high hardness of hard-coated films, such as antiglare properties and an increase in haze value, have been proposed, as disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 11-286083, 2000-326447, 2001-194504, and 2001-264508.
JP-A No. 11-286083 discloses an antiglare film comprising a transparent substrate film and a hard-coating layer that is formed on the transparent substrate film and mainly composed of particles with an average particle size of 0.6 to 20 μm, fine particles with an average particle size of 1 to 500 nm and a hard-coating resin. It also discloses that the thickness of the hard-coating layer is at most the particle size of the particles, preferably at most 80% of the average particle size (specifically at most 16 μm). However, such a thickness of the hard-coating layer has a problem in that sufficient hardness cannot be provided.
JP-A No. 2000-326447 discloses a hard-coated film comprising a plastic substrate film and at least one hard-coating layer formed on at least one side of the substrate film, wherein the hard-coating layer has a thickness of 3 to 30 μm, and the hard-coating layer contains inorganic fine particles with secondary particle sizes of at most 20 μm. It also discloses that the surface of the hard-coating layer is provided with unevenness so as to provide antiglare properties. Such a structure is, however, designed regardless of surface roughness of the hard-coating layer, and the structure having inorganic fine particles completely buried in the hard-coating layer has a problem in that sufficient antiglare properties cannot be provided.
JP-A No. 2001-194504 discloses an antireflection film comprising a plastic film and a laminate that is formed on at least one side of the plastic film and comprises a hard-coating layer and a thin antireflection film layer mainly composed of a metal alkoxide and a hydrolysate thereof, wherein the hard-coating layer has an elastic modulus of 0.7 to 5.5 GPa at its breaking strain or lower. It also discloses that the hard-coating layer has a thickness of 0.5 μm to 20 μm and that the hard-coating layer contains fine particles with an average particle size of 0.01 to 10 μm. According to the technique disclosed in JP-A No. 2001-194504, although hardness and scratch resistance can be improved, there is a problem in that fine particles are completely buried in the hard-coating layer and can not provide sufficient antiglare properties, for example, when fine particles with an average particle size of about 1.8 μm are added to a hard-coating layer with a thickness of about 20 μm.
JP-A No. 2001-264508 discloses an antiglare antireflection film comprising a transparent support and a laminate that is formed on the support and sequentially comprises an antiglare hard-coating layer containing particles with an average particle size of 1 to 10 μm and a low-refractive-index layer with a refractive index of 1.35 to 1.49 produced with a composition containing inorganic fine particles with an average particle size of 0.001 to 0.2 μm, a hydrolysate of a photo-curable organosilane and/or a partial condensate thereof, and a fluoropolymer, wherein the antiglare antireflection film has a haze value of 3 to 20% and an average reflectance of at most 1.8% at wavelengths of 450 nm to 650 nm. It also discloses that the antiglare hard-coating layer has a thickness of 1 to 10 μm. The invention disclosed in JP-A No. 2001-264508 has a problem in that sufficient hardness is not provided, while it is provided for the purpose of improving scratch resistance, antiglare properties or the like.